The present invention relates to pipe bending machines and more particularly concerns methods and apparatus for rapidly and accurately positioning a pipe for making a plurality of bends in accordance with given bend data.
In the bending of pipes, and particularly in the bending of automobile exhaust pipes, it is necessary to make a plurality of bends in the pipe with preselected relative positions, orientations and bend magnitudes. The finished pipe must have each bend located at a given longitudinal position with respect to an end of the pipe. Each bend must lie in a predetermined plane with respect to the planes of other bends and each bend must have a predetermined depth or angle of bend. The data defining these bend parameters, longitudinal position, plane of bend or pipe rotation and depth of bend or angle of bend is predetermined in any one of a number of ways. The data may be calculated from known equipment with which the pipe is to be employed, a sample pipe may be bent to fit the known equipment and the pipe may then be measured to provide the data, or an existing pipe may be measured to provide the given bend data.
Many bending machines are automated either completely or in varying degrees so that the given bend data may be programmed into a machine control and the machine operated under control of its program to automatically produce a series of bends in a pipe. An exemplary automatically controlled tube bending machine is shown in the patent to Hill U.S. Pat. No. 3,145,756. Such machines are complex and expensive and in many situations their cost, as compared to manually controlled machines, cannot be economically justified. Further, there are many manually controlled machines presently used which do not warrant replacement with automatic machines.
In typical manually controlled machines the pipe is moved by hand to a longitudinal position of the first bend and rotated by hand so that the bend will be in a predetermined plane. An hydraulic drive for a ram die is manually initiated to cause the die to bend the pipe against restraining wing dies. Depth of bend or angle of bend in such a machine is often controlled by a switch actuator connected with the hydraulic ram and positioned to engage an adjustable length stop rod as the ram reaches a desired end of its bend motion travel. The switch is thus actuated when the bend has been accomplished to the given depth as determined by the depth of bend stop. The ram die is automatically returned to a starting position after having completed the first bend. The pipe is then positioned by hand in a second longitudinal position and rotated about its longitudinal axis to achieve the second plane of bend. The depth of bend stop rod is adjusted in length or, in machines such as shown in the patent to Streit U.S. Pat. No. 3,126,045, a rotatable support mounting a plurality of preadjusted depth of bend stop rods is then moved to position the next stop rod in the path of the ram die limit switch. Then the second bend is completed by manually starting the hydraulically driven ram die. In some cases, as in the patents to Lance U.S. Pat. Nos. 3,339,385 and 3,581,537, and the patent to Ignoffo U.S. Pat. No. 3,388,574, the depth of bend is controlled by stops or tabs positioned on the wing dies so as to stop the motion of the ram die when the wing die has rotated through a predetermined angle.
In the past given bend data for use in manually controlled machines has been employed in a laborious, timeconsuming and imprecise manipulation of mechanical elements that provide physical stops to properly position the pipe both longitudinally and rotationally. Errors and lack of precision in machine set up are frequent and variable at least in part because of the number and type of specific adjustments that must be made by hand. Commonly the bending machine is a press type bender in which a ram die is hydraulically driven in a direction normal to the axis of the pipe to be bent and the pipe is bent between the ram and a pair of pivotally mounted restraining wing dies. The pipe to be bent is supported upon a long pipe bed adjacent the bending die. The pipe bed is provided with a number of adjustably mounted mechanisms that are positioned by the operator for set up of the manually controlled bending machine in accordance with the given bend data. Thus, a number of stops are slidably mounted on the pipe supporting bed and adjustably positioned longitudinally of the bed so that the pipe may be longitudinally positioned in abutment with the stops for each of a number of successive bends. A protractor type of device is often employed to position the pipe rotationally. In some devices of the prior art each of the longitudinal position stops also has a protractor so that an end of the pipe may be positioned in both longitudinal and rotational abutment with different ones of the stops in succession. In other devices linear or rotational scales are mounted directly upon the pipe supporting bed and various means are employed to facilitate positioning of the pipe with respect to such scales.
The patent to Zerlaut U.S. Pat. No. 3,336,776 employs a number of adjustable stop rings and associated electrical switch elements for correlating the rotational plane of bend and the motion of the ram die which determines the degree of bend.
In general, in the prior art arrangements for set up of a manually controlled bending machine, a large number of mechanical stops and one or more protractors are employed, and each of these elements must be manually positioned in accordance with given data. The manual positioning and adjustment of each of these elements not only requires a great deal of time and skill of an operator but even so, results in significant errors in magnitude and position of the bends. Thus, it is common for an operator to bend a number of sample pipes before achieving one that has all of its bends within the allowable tolerances. The various stops are set up according to the given bend data and a first sample pipe is bent. This sample pipe is then measured and is normally found to be unsatisfactory whereupon adjustments are made in the positioning of the various stops in an attempt to decrease the measured error. A second pipe is then bent and this procedure of bending and measuring a pipe, adjusting the various stops and again bending, measuring and adjusting, may be continued for a large number of pipes and for several hours before a satisfactory positioning of the stops is finally achieved.
The expense and time involved in initial set up of a manually controlled bending machine is justified for long production runs but is not economically feasible when relatively small numbers of pipes of a given configuration are to be produced. For such small runs, one must either employ an expensive, automatic bending machine or significantly increase the cost of the resulting pipes due to the cost of the large amount of set up time.
Once the stops have been properly adjusted for production of an acceptable pipe of a long production run, a skeletal structure having a number of pipe abutting brackets is constructed adjacent the bending machine so that after each bend the pipe may be moved longitudinally and rotationally until an already bent portion of the pipe abuts one of the brackets of the skeletal structure. Such bracket has been positioned so that with a portion of the bent pipe in abutment therewith, the pipe is in proper position with respect to the bending dies for the next bend. This skeletal structure includes a number of brackets sufficient to position the pipe for all of the bends to be made therein, but can be adjusted only after going through the multiple trail and error bending of many sample pipes and adjustment of the stops and protractors.
Accordingly, it is an object of the present invention to facilitate set up of manually controlled pipe bending machines and to decrease the time of set up of such pipe bending machines.